Discrimination of soil losses between ridge and furrow in longitudinal ridge-tillage under simulated upslope inflow and rainfall

Longitudinal ridge-tillage greatly enhances hillslope soil erosion due to increased flow concentration in furrows and sediment delivery from ridge sideslopes. Currently, contributions of upslope inflow and rainfall to soil loss and identification of sediment sources in a ridge-furrow system are still unclear. A set of experiments on 10-m long, 2-m wide field runoff plots at a 5 degrees slope gradient were conducted in the Chinese Mollisol region to quantify the effects of upslope inflow and rainfall on hillslope erosion and to discriminate sediment contributions between ridges and furrows in a longitudinal ridge-tillage system. The experimental treatments included five upslope inflow rates alone (10, 20, 30, 40 and 50 L min(-1)), two rainfall intensities alone (50 and 100 mm h(-1)) and the five inflow rates combined with the two rainfall intensities. A stereoscopic photogrammetry method was used to measure micro-topographic conditions before and after each run. The results showed that, compared with the inflow-only treatments, soil losses increased by 1.4-5.2 times and 2.5-14.0 times under the combined treatments of the five inflow rates and two rainfall intensities, respectively. The contributions of the synergistic effects increased with the increase of rainfall intensity. Moreover, in the five upslope inflow-only treatments, soil erosion mainly occurred in the bottom of furrows and ridge toe slopes; while for the combined treatments, ridge sideslope erosion dominated as soil loss from ridge areas accounted for 51.3 %-60.9 % and 53.0 %-61.8 % for the 50 and 100 mm h(-1) rainfall intensities, respectively. Therefore, ridge sideslope erosion may be the main sediment source in the longitudinal ridge-tillage system under the bare conditions.